Pete's Big Fuse location and other fix thread

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okstrat

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I see this a lot... and I had one of my RM100s on the bench, thought I'd take a few pics of the guts and show you guys a few places to check if you're having issues. A few things before we start though:

I and Ned and ANYONE involved with this board take no responsibility if you go digging around in your amp and hurt yourself. If you don't think you should be troubleshooting your amp, then go take it to a tech. Don't try to save a few bucks and hurt yourself in the process. There can be lethal voltages in a guitar amp and I can't cover every possiblity or eventuality in this thread - YOU USE ANY INFORMATION IN THIS THREAD AT YOUR OWN RISK.

Unplug the amp from the power supply.

First off, is the amp totally dead? Then take a small flat blade screwdriver and remove the fuse cover next to the power cord. BE SURE YOU DO NOT CHANGE THE POSITION OF THE FUSE COVER - Your voltage should be top center. Don't change this! Mine was 120v, for example.

mainfuse.jpg


Pop the cover off, pull out the fuse, and check it with a multimeter. I use one that can be set to make a noise when there is continuity - place a probe on each end of the fuse and see if your meter reacts the same as if you were touching the probes together. If so, then the fuse is passing current and you're ok. Fuses can be obviously burnt and bad, but sometimes they look good but are bad. Testing with a meter is the best way.

mainfuse2.jpg


Now take the amp chassis out of the enclosure. If you need help figuring this out, it may not be a good idea for you to go any further.

Discharge the capacitors at this point. If you don't know how to do this, look it up. Google is your buddy. If you don't want to take the time to do this, take the amp to a tech.

All the fuses other than the main fuse we looked at and the individual tube fuses are all in a cluster near the midi jacks. You will have to remove the midi board to get to two fuses underneath it. Take the two screws out, and there is enough wire to move the board over and away.

midiboardremoval.jpg


Note the dip switches on the midi board for setting channels...

midiboard.jpg


Here's a pic with the midi board moved, of all 7 of the fuses. 4 and 5 were hidden under the midi board. Remove and test each one, if one is bad - replace it with the same value and type. NEVER put a fuse larger than specified in any device. Bruce Egnater has stated we can use 400ma fuses for the tube fuses, but I would leave all the other ones alone value-wise.

fuse-locations.jpg


While you're in there, look at any spade connectors. If you've had a speaker cab open, usually they use connectors like this for the speakers. Be sure all of them you can see are tight and pushed on the terminals correctly. This pic is of the standby and power switches - mine came loose on a standby switch and the amp wouldn't come out of standby. It just had a loose connector.

standbyswitch.jpg


More to come later, I'm beat. :)

Pete
 
Pete once again.....your info is GOLDEN!! You been a big help when my RM100 was "dead"....it was those darn eternal fuses!!
Not really that hard to get at them but I was nervous to be poken around inside. Your info helped alot. :p

Dan
 
Pete..here's a thought, why not post the Fuse types, sizes and rating.

The only one I know is the external tube fuses:

Glass 5x20mm Fast Blo 250V/400mA (stock was 250 or 315...they now ship with 400)

and main external fuse

50W
Glass 5x20mm Slo Blo 250V/3A (at 100/120V), 1.5A (at 220/240V)

100W
Glass 5x20mm(?) Slo Blo 250V/5A (at 100/120V), 2.5A( at 220/240V)
 
What about the RM 50? Is everything the same? I have an RM 50 coming this week so I have loads of interest in this info. 8)
 
what are the values for the fuses on the midi board? fuse 7 went out on me and im not getting any bites to the thread i made asking..
 
Same question:

mine just said "250V"
but how many amps? 1 amp....2 amp...
What would be a safe bet on these eternal fuses?
My RM100 took a dive on me again. I get power....fan comes on.....but no lighting of the tubes. One of the fuses was burned out (The fuse you marked #1) I tried to replace it with other fuses that were 250V and no luck.
I checked all the other fuses and they pass the multi meter test. Not sure what the deal is or could be. I will have to tinker around with it later today. I was just getting frustrated last night and decided to stop until the next day and come in with new eyes. Any suggestions guys?
This happened before to me but I just pulled the fuses and re-set them and it fired right up. Stumping me this time.

Dan :?
 
Ok....just brang my amp back from the DEAD! :?
One of the eternal fuses. With some guidance from Pete found a seller on the web(mouser) and thank god! I could not find these things locally to save my life. I totally understand about not wanting to give out the wrong values for the fuses since you can REALLY break something inside that amp if the wrong is used. Lucky to have this board and lots of cool people helping me to get the parts I needed. Shame a 95 cent fuse can shut down the whole amp! But the one I had to replace was the one that send the signal or heat to light up the power tubes. I had power to my amp but the tubes werent firing up. the fuse I replaced was 10 amps 250 volts in that little fuse! :shock:
But once the parts came in today....popped it in. Did a test power up....tubes started to glow(YES!!) so I slapped it back together, did a Bias and a quick run on the amp. Sounds and playing perfect.
Just wanted to share my woes and griefs with you all. I am getting pretty good at taking the amp apart but I would rather leave it up to the experts. Like Pete mentioned, if your amp "dies" chances are its one of the 7 eternal fuses.
Rock on!! 8)
 
Man I wish those fuses were eternal :) Am guessing you meant internal ??? :?

'grats on being up and running again.
 
JKD said:
Man I wish those fuses were eternal :) Am guessing you meant internal ??? :?

'grats on being up and running again.
+1000 on that!
I was having a brain fart! Yes...wish they "lived forever" myself!
So eternal INTERNAL fuses.....who makes them?? :p
 
pete or anyone else in the know ,are the fuse locations the same for a T2 as in the above pics of the rm?
i have lost all sound from mine but the tubes are all still good so i think it mite be a fuse?
any suggestions ?
 
teetoo said:
pete or anyone else in the know ,are the fuse locations the same for a T2 as in the above pics of the rm?
i have lost all sound from mine but the tubes are all still good so i think it mite be a fuse?
any suggestions ?
Have you had the chassis out of the head shell?
 
Guys, I have searched and found nothing about the values of the internal fuses, can someone help here... I took them out but I can't read the fuse rating... I would really appreciate any help... I have this Randall unused for 6 months... using a Triaxis ... is not just fair :evil: I know is something minor maybe cause by a tube but I just cant replace them... I am afraid I put something of wrong value and really **** this amp
 
Here is the response I got from Randall but I can't seem to identify properly which one corresponds to the pictures attached by Pete.

TUBE: (4) .400mA amp FAST BLO OR REGULAR YES.

MAIN: (2) 10A TUBE HEATER FUSES

MIDI: 1.5 or 2A.

INLET: 5A

SUPPLY: (2) 1.6 AND (2) 5A


Which ones are the MIDI fuses, the Inlet? and Supply?

PLEASE HELP... I WANT TO FIX THIS S.O.B. WHAT A TERRIBLE DESIGN... WHAT THEY WERE THINKING?? THAT OWNERS LOVE TO PUT THEIR LIVES ON RISK BY SWITCHING FUSES NOT PROPERLY ASSIGNED ???
IT IS REALLY A SHAME... I WENT BACK TO MESA BOOGIE AFTER THIS...
I HAVE NEVER BLOWN A MESA BOOGIE FUSE NOR I HAVE TO TOOK THE AMP APART....
:x :x :x :x :x
 
joeymex said:
Here is the response I got from Randall but I can't seem to identify properly which one corresponds to the pictures attached by Pete.

TUBE: (4) .400mA amp FAST BLO OR REGULAR YES. = Externally accesible beneath power tubes

MAIN: (2) 10A TUBE HEATER FUSES = F3 and F4 (1 and 2 on teh diag)?

MIDI: 1.5 or 2A. (I believe this is the big red cylinder pictured on the midi board)

INLET: 5A = externally accessible and next to mains cable

SUPPLY: (2) 1.6 = F1G and F2G (5 and 4 on teh diag) AND (2) 5A = F3G and F4G (6 and 7 on the diag) ?


Which ones are the MIDI fuses, the Inlet? and Supply?

PLEASE HELP... I WANT TO FIX THIS S.O.B. WHAT A TERRIBLE DESIGN... WHAT THEY WERE THINKING?? THAT OWNERS LOVE TO PUT THEIR LIVES ON RISK BY SWITCHING FUSES NOT PROPERLY ASSIGNED ???
IT IS REALLY A SHAME... I WENT BACK TO MESA BOOGIE AFTER THIS...
I HAVE NEVER BLOWN A MESA BOOGIE FUSE NOR I HAVE TO TOOK THE AMP APART....
:x :x :x :x :x

You misunderstand the purpose of fuses...they are there to sacrifice themselves before something either presents a hazard and/or further damage occurs.

If a user is not comfortable servicing an amp then they should give it to a tech.

In the above list, the bias supply (F1 or Fuse 3 in the diag) appears to be missing but it's 250mA fuse I believe.

Have you identified which of teh fuses is defective by using a meter? I've download the cad stuff and can read the values directly if you tell me which of the fuses you have found to be bad...

Please note that you could replace the fuse and it could simply blow again as the condition that caused it is still there...
 
If any of you have a schematic it shows the fuse value in the schematics.
It shows that F1 is 1.6Asb, F2 is 1.6Asb, F3 is 5Asb, F4 is 5Asb
A = amp, sb = slow blow
 
any idea what these internal (eternal haha) fuses do? my fx loop is acting funky. visually the fuses look good but i'd need to get them tested as my multimeter continuity function isnt working
 
JKD said:
Pete..here's a thought, why not post the Fuse types, sizes and rating.

The only one I know is the external tube fuses:

Glass 5x20mm Fast Blo 250V/400mA (stock was 250 or 315...they now ship with 400)

and main external fuse

50W
Glass 5x20mm Slo Blo 250V/3A (at 100/120V), 1.5A (at 220/240V)

100W
Glass 5x20mm(?) Slo Blo 250V/5A (at 100/120V), 2.5A( at 220/240V)

By "main external fuse" do you mean the one next to the power cord jack? I thought I understood that to be the case until I went to the second page of this thread. On the next page "joeymex" wrote:

"Here is the response I got from Randall but I can't seem to identify properly which one corresponds to the pictures attached by Pete.

TUBE: (4) .400mA amp FAST BLO OR REGULAR YES.

MAIN: (2) 10A TUBE HEATER FUSES

MIDI: 1.5 or 2A.

INLET: 5A

SUPPLY: (2) 1.6 AND (2) 5A

Which ones are the MIDI fuses, the Inlet? and Supply?"

My RM100LB is down and it looks like the fuse, that I would call the "main external fuse" looks fried; the one next to the power cord jack.
 
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